Polymers flocculation prevention

Surfactants have also been used to overcome the solubility limitation of synthetic polymers in CO2 (most common synthetic polymers would be considered to be C02-phobic). For example, surfactants have been used to aid in the dispersion polymerization of poly(methylmethacrylate) (PMMA) in CO2 (58-60). The surfactants used in the polymerizations of PMMA are more accurately referred to as stabilizers. The C02-phobic region acts as anchor to the growing polymer, either by physical adsorption or by chemical grafting. The C02-philic region sterically stabilizes the growing polymer particles, preventing flocculation and precipitation. When a biopolymer is not soluble in CO2, specific surfactants may be designed to aid in the solubilization of the polymer into CO2. 

Li-in-on et al. (1975) were the first to publish compelling experimental evidence which showed that relatively high concentrations of free polymer could prevent particles from undergoing flocculation. These observations... 

In dispersions of particles and nonadsorbing polymer, flocculation may be induced at certain concentrations (11). At low concentrations the presence of free polymer has no effect on the dispersion stability, but as the concentration is raised flocculation occurs. As two particles approach each other, at separations corresponding to twice the radius of gyration of the polymer, polymer becomes excluded from the volume of solution between the particles. The particle separation is such that polymer is prevented from entering the interparticle space. The gap can now be considered as an osmotic membrane, permeable only to solvent molecules. The bulk solution thus exerts a compressive osmotic pressure and solvent drains from the space between the particles causing the particles to flocculate. 

In some systems, such as lake and river waters, the suspended inorganic particles may be coated by biological polymers, termed humic substances, which prevent flocculation by either steric or electrostatic mechanisms. These can also interact with added inorganic salts (31) that can neutralize charged functional groups on these polymers. 

Low molecular cationic polymers or alum can also be used to flocculate pitch, ie, bind up the pitch so that it is retained in the sheet, to minimize pitch deposition on machine surfaces and fabrics (35,36). Alum is used commonly in newsprint operations (34). The addition of a nonionic surfactant with a hydrocarbon solvent to the wet end has shown some utility in preventing deposits of adhesive recycled furnish contaminants from forming on the paper... 

Most synthetic latices contain 5—10 wt % of nonelastomeric components, of which more than half is an emulsifier or mixture of emulsifiers. One reason for this relatively high emulsifier concentration as compared with natural latex is that emulsifier micelles containing solubiHzed monomer play a principle role in the polymerization process. A high emulsifier concentration is usually necessary to achieve a sufficiently rapid rate of polymerization. Secondly, a considerable fraction of the surface of the polymer particles must be covered by adsorbed soap or equivalent stabilizer to prevent flocculation... 

Polymers are suspended as microparticles in the latex and interactions between these microparticles are prevented by the presence of adsorbed suspending agent and soap molecules. Blending results in a random suspension of dissimilar particles in the mixture of latexes, each unaffected by the other. Rate of flocculation depends entirely on the stabilizer and not on the polymer characteristics as such. Coagulated mass contains an intimate mixture of the polymers. Acrylonitrile butadiene styrene (ABS) polymers [23-25] may be prepared by this method. 

Copolymers or terpolymers of acrylic acid, which contain from 5 to 50 mole-percent of sulfoethyl acrylamide, acrylamide and sulfoethyl acrylamide, ethyl acrylate and sulfoethyl acrylamide, acrylamide and sulfophenyl acrylamide, and acrylamide and sulfomethyl acrylamide, are claimed to be calcium-tolerant deflocculants for drilling fluids [704]. In general, 0.1 to 2 lb of polymer per barrel of drilling fluid is sufficient to prevent flocculation of the additives in the drilling fluid. 

Thinners and dispersants are used to prevent excessive flocculation of clay particles and maintain pumpability of the fluid. Tannins, various lignosulfonate salts, sodium tetraphosphate and other phosphates, and synthetic polymers such as sodium poly(styrene sulfonate-co-maleic anhydride) have been used. 

The polymer radius has to be larger than 80% of the particle radius to avoid adsorption limitation under orthokinetic conditions. As a rule of thumb a particle diameter of about 1 pm marks the transition between perikinetic and orthokinetic coagulation (and flocculation). The effective size of a polymeric flocculant must clearly be very large to avoid adsorption limitation. However, if the polymer is sufficiently small, the Brownian diffusion rate may be fast enough to prevent adsorption limitation. For example, if the particle radius is 0.535 pm and the shear rate is 1800 s-, then tAp due to Brownian motion will be shorter than t 0 for r < 0.001, i.e., for a polymer with a... 

Although the production of highly deflocculated suspensions is a primary objective for formulation of suspension concentrates, these systems tend to settle under gravity forming dilatant sediments (clays). The latter must be prevented either by controlled flocculation or by the addition of a second disperse phase to the continuous medium (1). One method which may be applied to sterlcally stabilised dispersions, is to add a free (ie. non-adsorbing) polymer to the continuous medium. 

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